Rockwell Automation 1747-ASB Remote I/O Adapter - Manual (Page 139)

Publication 1747-UM006B-EN-P - June 2003
Specifications A-11
1. T
dm-nbt
equals 80ms
(1)
for a specific pair of discretely mapped
input and output modules. The maximum throughput for these
discretely mapped I/O modules when block transfers are
present are:
T
dm-bt
= T
dm-nbt
+ 2T
btx
T
dm-bt
= 80ms + 2T
btx
2. Determine the maximum length of the block transfer to each
logical device. There are two logical devices for the 1747-ASB
module. The largest block transfer that is possible with the full
logical rack, logical device is 8 words. The largest block
transfer that is possible with the 1/2 logical rack, logical device
is 2 words.
3. Substitute the maximum length of each logical device into:
T
ri
= 0.150 x block transfer length + 3.5ms
T
ri
= (0.150 x 8 ) + 3.5ms
T
ri1
= 4.7ms
T
ri
= (0.150 x 2 ) + 3.5ms
T
ri2
= 3.8ms
4. There is one logical device for each 1771-ASB module. The
largest block transfer for 1/4 logical racks is 64 words. Calculate
the maximum length for these logical devices:
T
ri
= 0.150 x block transfer length + 3.5ms
T
ri
= (0.150 x 64 ) + 3.5ms
T
ri3 & 4
= 13.1ms
5. Add up all of the maximum word lengths:
T
btx
= T
ri1
+T
ri2
+ T
ri3
+ T
ri
4
T
btx
= 4.7+ 3.8 + 13.1 + 13.1
T
btx
= 34.7ms
(1) This number is arbitrarily assigned.